1. Field of the Invention
The present invention relates to the structure of a pivot portion of a rear swing arm of a motorcycle.
2. Description of the Background Art
A pivot structure of a rear swing arm of a motorcycle is known in which a pair of left and right pivot plates made of iron are used. Front ends of a rear swing arm are placed between the left and right pivot plates, and coupled by a pivot bolt. An adjusting collar is installed at a bolt through hole of one of the pivot plates (refer to JP-A-62-60491U).
The above-described pivot structure is a structure fastened together by an axial force produced by a bolt-and-nut coupling. The adjusting collar is present and therefore, deformation of the left and right pivot plates can be reduced. However, when the pivot plates are arranged on inner sides of the rear swing arms, such a fastening structure cannot be adopted. Therefore, there is desired an adjusting mechanism which may be used even in an arrangement where vehicle body frame members such as pivot plates are arranged on inner sides of rear swing arms.
Further, in the case of a backbone type vehicle frame, when it is of a type in which rear swing arms are interposed between a pair of left end right pivot plates, other parts of a carburetor and the like are difficult to lay out without interfering with the vehicle body frame and therefore, integral formation of a center frame is also desired.
Further, in view of promoting frame rigidity, it would be desirable to also connect a crankcase of an engine at the pivot portion along a single axis. The present invention resolves such problems.